Redis Pub/Sub and Streams answer different delivery questions. Pub/Sub broadcasts to currently active subscriptions without retaining messages for later replay. A stream stores entries that readers can revisit while they remain retained. Choosing between them starts with who must receive an event and what should happen during a consumer’s absence. ...
Replay needs retained records: schematic.
A Redis stream stores entries under ordered IDs so readers can revisit retained history. Unlike Pub/Sub, the reader need not be online when the producer appends. That difference provides replay, not unconditional durability: deleted entries, retention limits, and persistence settings still determine what remains available after delay or failure. ...
Pub/Sub has no replay: schematic.
Redis Pub/Sub broadcasts to subscriptions that are active when a message is published. It does not retain an inbox for a disconnected listener. This suits replaceable live notifications, but a positive PUBLISH response is not evidence that a worker finished a job or that an offline consumer can recover it. ...